Institute of Electrical and Electronics Engineers (IEEE) and Internet Engineering Task Force (IETF) has defined network node capabilities for performance and fault management through the means of Operations, Administration and Management (OAM) protocols. In general, such protocols are handled by two types of entities located on the network node; Maintenance End-Points (MEP) and Maintenance Intermediate Points (MIP). The MEPs are located at the Ingress and egress of a network path, a tunnel, a virtual circuit, a link or a service. The MIPs are situated at the nodes that are part of the network path between the ingress and egress of the network path. Currently, the MEPs are active, which means that they can initiate measurement sessions. In contrast, the MIPs are passive, which means that they may only reply to requests or forward measurement packets that are not addressed to them.
The OAM tools for fault management and performance analysis are based on the standardization work of IETF and the International Telecommunication Union (ITU). For example, recommendations for Ethernet OAM functions are given in ITU-T Rec. Y.1731, titled “OAM Functions and Mechanisms for Ethernet Based Networks”, issue February/2008. For Multi-Protocol Label Switching Transport Profiles (MPLS-TP), performance measurements are defined in RFC 6374, titled “Packet Loss and Delay Measurement for MPLS Networks” to D. Frost and S. Bryant, dated September 2011. For Internet Protocol (IP) networks, a so called trace-route tool is specified in RFC 1393, titled “Trace-route Using an IP Option” to G. Malkin, Network Working Group, from 1993.
An overview of existing OAM protocols for fault management and performance monitoring at different layers, e.g. MPLS, IP, and Ethernet, is presented in IEEE Communications Magazine, vol. 43, pp. 152-157, November 2005, “Ethernet OAM: Key Enabler for Carrier class Metro Ethernet Services” to M. McFarland, S. Salam, and R. Checker. In this overview, necessary usage requirements in the continued standardization work of the protocols are discussed.
With existing OAM tools localization of performance degradations on segments between MIPs is cumbersome due to additional measurements. In many cases, it is even impossible to achieve such localization of performance degradations or anomalies on links between MIPs.
FIG. 1 shows a known network, comprising MEPs and MIPs. The MIPS are shown as triangles. An expected success rate E for links Y1 to Y4 is to be determined by use of a trace-route tool. A link, see Y4, comprises segments X1 to X4.
Table 1 shows an exemplifying result from a trace-route tool when run in the network of FIG. 1. The first column of table 1 presents the number of the segment, i.e. the number of each of X1 to X4. The following three columns comprise the delay measured between the MEP and a particular MIP, e.g. the links Y1 to Y4. The numbering of the segments coincides with numbering of MIPs. Sometimes a MIP is referred to as a hop. Though, the last hop is the egress MEP for the trace-route tool. A segment may sometimes be referred to as a hop. Letters A through J represent IP-addresses, such as 66.249.95.219, www.mydomain.com, for different MIPs.
TABLE 1Output from a known trace-route toolHop #T1 (ms)T2 (ms)T3 (ms)MIP11911A2111B3222C4244022D5322E6222223F7272G8332H9222222I10212121J
For hop 4 in the left-most column, it can be observed that some of the probe packets exhibit a significantly higher delay than other probe packets, i.e. 40 ms, compared to 22-24 ms. A similar artifact is exhibited on line 7, where we have 7 ms compared to 2 ms. If a network operator tries to determine which segment is responsible for the increase in delay, the information made available by the trace-route tool is not enough in order to do an unambiguous identification of the segment, or segments, where the degradation occurred.
In the example above, an operator may conclude that the segments between MIPs 3-4 and 6-7 are degraded. However, such a judgment actually disregards the fact that the trace-route probe packets are sent individually at pre-defined intervals and thus encounter different network conditions. Hence, a degraded segment, e.g. in the form of a transient problem, observed due to report of delayed packet to MIP 4 may have finished by the time another packet, which was sent to MIP 7, arrives.
Therefore, a problem in relation of the example above is that manual processes for identifying segments responsible for performance degradations in packet networks are error-prone and provide ambiguous results.
Furthermore, it is known to operate OAM tools proactively. This means that the OAM tool is run periodically, with a fixed time interval that is configured when the OAM tool is installed into a network. The fixed time interval is kept constant as long as the proactive operations mode is enabled. With a short fixed time interval, a high rate of invocations of the tool is obtained. The network is then loaded with traffic, generated by the OAM tool. Hence, performance, in terms of capacity for other traffic than that generated by the OAM tool, is degraded. Oppositely, a low rate of invocations of the OAM tool is likely to miss degradations that were short-lived, but still may affect performance of the network negatively.
According to known solutions, the above mentioned problem may be solved by the provision of dedicated probing nodes. This means that the MIPs and MEPs are replaced by the dedicated probing nodes, each of which includes dedicated management software.
In case an OAM tool, based on the above mentioned Y.1731 for Ethernet OAM functions, is employed, the dedicated probing nodes cannot be used, because the MEPs cannot be placed on the data plane other than on the ingress and egress of a particular tunnel, such as an E-LINE. Moreover, the use of dedicated probing nodes is rather expensive to install and operate. In addition, planning with respect to the placement of the probing nodes within the network is required. Attempts in applying methods resembling dedicated probing have been done as in e.g. http://www.jdsu.com/ProductLiterature/EthernetAccess_TN_CPO_TM_AE.pdf.Disadv antageously, flexibility of the network is also reduced, since the placement of the probing nodes needs to be re-planned in response to any changes in the topology of the network.